protocol.go

// Copyright 2023 PingCAP, Inc.
// SPDX-License-Identifier: Apache-2.0

// The MIT License (MIT)
//
// Copyright (c) 2014 wandoulabs
// Copyright (c) 2014 siddontang
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software is furnished to do so,
// subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// Copyright 2013 The Go-MySQL-Driver Authors. All rights reserved.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.

package net

import (
	"bytes"
	"io"
)

func ParseLengthEncodedInt(b []byte) (num uint64, isNull bool, n int) {
	switch b[0] {
	// 251: NULL
	case 0xfb:
		n = 1
		isNull = true
		return

	// 252: value of following 2
	case 0xfc:
		num = uint64(b[1]) | uint64(b[2])<<8
		n = 3
		return

	// 253: value of following 3
	case 0xfd:
		num = uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16
		n = 4
		return

	// 254: value of following 8
	case 0xfe:
		num = uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16 |
			uint64(b[4])<<24 | uint64(b[5])<<32 | uint64(b[6])<<40 |
			uint64(b[7])<<48 | uint64(b[8])<<56
		n = 9
		return
	}

	// https://dev.mysql.com/doc/internals/en/integer.html#length-encoded-integer: If the first byte of a packet is a length-encoded integer and its byte value is 0xfe, you must check the length of the packet to verify that it has enough space for a 8-byte integer.
	// TODO: 0xff is undefined

	// 0-250: value of first byte
	num = uint64(b[0])
	n = 1
	return
}

// SkipLengthEncodedInt skips the int and only returns the length of the encoded int.
func SkipLengthEncodedInt(b []byte) int {
	switch b[0] {
	case 0xfc:
		return 3
	case 0xfd:
		return 4
	case 0xfe:
		return 9
	default:
		return 1
	}
}

func ParseLengthEncodedBytes(b []byte) ([]byte, bool, int, error) {
	// Get length
	num, isNull, n := ParseLengthEncodedInt(b)
	if num < 1 {
		return nil, isNull, n, nil
	}

	n += int(num)

	// Check data length
	if len(b) >= n {
		return b[n-int(num) : n], false, n, nil
	}

	return nil, false, n, io.EOF
}

func ParseNullTermString(b []byte) (str []byte, remain []byte) {
	off := bytes.IndexByte(b, 0)
	if off == -1 {
		return nil, b
	}
	return b[:off], b[off+1:]
}

var tinyIntCache [251][]byte

func init() {
	for i := 0; i < len(tinyIntCache); i++ {
		tinyIntCache[i] = []byte{byte(i)}
	}
}

func DumpLengthEncodedInt(buffer []byte, n uint64) []byte {
	switch {
	case n <= 250:
		return append(buffer, tinyIntCache[n]...)

	case n <= 0xffff:
		return append(buffer, 0xfc, byte(n), byte(n>>8))

	case n <= 0xffffff:
		return append(buffer, 0xfd, byte(n), byte(n>>8), byte(n>>16))

	case n <= 0xffffffffffffffff:
		return append(buffer, 0xfe, byte(n), byte(n>>8), byte(n>>16), byte(n>>24),
			byte(n>>32), byte(n>>40), byte(n>>48), byte(n>>56))
	}

	return buffer
}

// DumpLengthEncodedString dumps string<int>.
func DumpLengthEncodedString(buffer []byte, bytes []byte) []byte {
	buffer = DumpLengthEncodedInt(buffer, uint64(len(bytes)))
	buffer = append(buffer, bytes...)
	return buffer
}

func DumpUint32(buffer []byte, n uint32) []byte {
	buffer = append(buffer, byte(n))
	buffer = append(buffer, byte(n>>8))
	buffer = append(buffer, byte(n>>16))
	buffer = append(buffer, byte(n>>24))
	return buffer
}

func DumpUint16(buffer []byte, n uint16) []byte {
	buffer = append(buffer, byte(n))
	buffer = append(buffer, byte(n>>8))
	return buffer
}